There is an increasing demand for the most accurate possible three-dimensional representation of the appearance and pattern of vessels in parts of the body, in particular of arteries and veins, for diagnostic purposes within the field of vascular diseases and the therapy thereof. The examination of cerebral aneurysms represents an important field of application; this also includes an analysis and optimal representation for defining the aneurysm neck using topographical relationships with adjacent vessels. Angiographs are also carried out on other parts of the body, in order to determine arteriosclerotic changes or deformities. The introduction of computer-aided rotation angiography, which reconstructs three-dimensional representations with an equal resolution from the projection raw data, achieves a technical breakthrough within the field of diagnostics.
So-called C-arm angiographs form the prior art here, in which an x-ray source and a sensor arranged opposite thereto are rotated about the part of the body of a patient to be examined in an arc encompassing approximately 200° with between 50 and 500 x-ray images being recorded and digitally stored in the process. A three-dimensional model of the x-rayed part of the body can be calculated from the projection x-ray images recorded from different projection angles. Conventional 3D angiography nevertheless fails to ensure adequately clear separation between the arterial and venous vascular systems, by virtue of the recording times and the dynamics of contrast agent propagation.
With the already known three-dimensional vascular representation, a so-called mask pass and a filler pass are recorded. During the mask pass the C-arm rotates about the examination object and x-ray images are recorded over the predetermined angular range. A contrast agent is then injected into the vessel of interest and with another C-arm rotation, the so-called filler pass, a second set of x-ray images is recorded. The projection data of both image sequences is now subtracted from one other such that only the contrasted vessels (i.e. containing contrast agent) can still be seen in the result. These are now reconstructed to form a three-dimensional data record using a 3D reconstruction method. Alternatively masks and filler pass data can also be reconstructed separately and the resulting three-dimensional data records subtracted from one another.
The 3D angiography method according to the prior art generally provides a three-dimensional data record, which represents both a part of the arterial vascular system as well also as parts of the venous vascular system. The reason for this shortcoming in current angiography systems can be attributed to the rotation time of the tomograph of around 5 s being significantly longer than the so-called arterial phase of vascular contrasting, which only lasts 2 to 3 seconds. The contrast agent then migrates via the usual capillary paths into the venous vascular system so that a venous phase of the vascular contrasting is shown after the arterial phase has passed, said vascular contrasting being recorded in a subsequent part of the rotation of the tomograph, thereby resulting in a three-dimensional mixed structure of arteries and veins.